Conventionally, powders, which are typically exemplified by pigments, have been used in a variety of applications including cosmetics, paints, inks, pencils, memory materials, lubricants, medicines, and foods, and various studies have been performed to obtain stable dispersion. In order to disperse uniformly the powders such as pigments in oily components, it is required to improve the wettability of the powders, thereby inhibiting aggregation of the powders and stabilizing the dispersion. Extensive studies have been conducted to achieve these objects.
For example, in the field of cosmetics, powders such as pigments are blended thereinto so as to provide a desired color to the cosmetics, and to improve sense of use. For this reason, in order to provide cosmetics of stable quality, it is necessary to uniformly and stably disperse powders such as pigments in oily components. As a way of improving the dispersibility of the pigment itself, for example, there has been performed a treatment of a surface of a pigment with a silane coupling agent, etc. However, if the degree of surface treatment is increased, although the dispersing ability is improved, there are problems in that the cosmetics blended with such a pigment give poorer fitting to skin, and when used for a prolonged period of time, floating, unevenness, or the like, of cosmetics is caused.
On the other hand, an attempt has been made to uniformly disperse a pigment in oily components by using as a pigment dispersant a polar oil in which a hydroxyl group remains and further using a pigment in combination with the pigment dispersant. For example, as a pigment dispersant, there is known diglyceryl triisostearate (see Patent Document 1), or sucrose fatty acid esters such as sucrose stearic acid ester and sucrose oleic acid ester.
[Patent Document 1] Japanese Laid-Open Patent Application No. 2001-158718
However, the invention as described in Patent Document 1 limits the amount of a pigment to be blended to 30% by mass or less, and from the review of Examples, the amount of the pigment dispersant required to satisfy the pigment dispersibility is assumed to be around 20% by mass. Recently, various qualities are required for cosmetics, and the role of the pigment selected to be blended is increasingly becoming important. In addition, the amount of pigment to be blended tends to increase. If the amount of pigment to be blended into the cosmetics is increased, there occurs aggregation of the pigment, etc., thereby causing a problem such as deterioration of dispersibility. In the case of using a conventional pigment dispersant, as the amount of the pigment to be blended is increased, the amount of the pigment dispersant to be blended should be increased, correspondingly. However, since it is also required to blend other components (for example, an oil gelling agent, a feeling improving agent, a moisturizer, and cosmetic components) in the cosmetics, there are problems such that there is a limit in the amount of each of the pigment dispersant and the pigment to be blended, respectively, and that it is difficult to satisfy both of the pigment dispersibility and the sense of use, etc. at the same time.
In addition, although sucrose stearic acid ester has excellent dispersion ability, it is mostly in the state of a solid form having high crystallinity. Thus, if the amount of esters blended in the cosmetics is increased, it is difficult to retain its own shape, for example, crystals precipitate over time. Furthermore, when a liquid sucrose oleic acid ester is blended into the cosmetics, rancidity is generated over time, thus causing an odor problem.
As such, a dispersant for pigments, etc., which provides various cosmetics excellent in the sense of use, make-up lasting, odor, stability over time, and the like, by being blended therewith, and realizes blending of powders in a large amount and has excellent dispersibility, is not yet found. In practice, conventional cosmetics have been developed under limitations in the blended amount of a pigment, etc.
If a dispersant for a pigment, etc. that can satisfy all of the above-described characteristics is developed, such a dispersant can be used in various applications including cosmetics, paints, inks, pencils, memory materials, lubricant, medicines, and foods, which require powders such as pigments to be blended therein, and further, it can be expected to develop a product having an excellent color tone or sense of use, that has an equivalent or higher content of powders than that of those conventionally used. Furthermore, if such dispersant is used for cosmetics, a cosmetic excellent in sense of use, make-up lasting, odor, stability over time, etc. can be provided. Therefore, in the field of cosmetics, it is expected that the problems which have not been overcome until now will be solved.